APPLY WEATHER INFORMATIONAPPLY WEATHER INFORMATION

The weather cannot be controlled, only The weather cannot be controlled, only prepared for…prepared for…

Assessment criteria:Assessment criteria:

Identify sources of weather informationIdentify sources of weather information Obtain & interpret meteorological dataObtain & interpret meteorological data

– Synoptic charts & satellite imagesSynoptic charts & satellite images– Daily & 4 day forecastsDaily & 4 day forecasts– Max & min temperaturesMax & min temperatures– Rainfall, snowfall, pressureRainfall, snowfall, pressure– warningswarnings

Weather maps and chartsWeather maps and charts

Atmospheric pressure map

Visible satellite image

Infra red satellite image

Source: Images from Japan Meteorological Agency satellite MTSAT-1R via Bureau of Meteorology.

Other types?

Assessment criteria:Assessment criteria:

Access area-specific informationAccess area-specific information Interpret BoM forecasts & warnings & Interpret BoM forecasts & warnings &

assess appropriateness of activities in assess appropriateness of activities in planningplanning

Access additional weather information as Access additional weather information as necessary for planningnecessary for planning– River heights, tides, snow coverRiver heights, tides, snow cover– Estimated water release from damsEstimated water release from dams

Assessment criteria:Assessment criteria:

Evaluate current & predicted weather Evaluate current & predicted weather conditions in terms of their effect on a conditions in terms of their effect on a planned outdoor activityplanned outdoor activity

Modify activity plans, if necessary, following Modify activity plans, if necessary, following consideration of weather informationconsideration of weather information

BACKGROUND WEATHER BACKGROUND WEATHER INFORMATION:INFORMATION:

SEASONSSEASONS UNIQUE AUSTRALIAN WEATHERUNIQUE AUSTRALIAN WEATHER PRESSURE SYSTEMSPRESSURE SYSTEMS AIR MASSES & FRONTSAIR MASSES & FRONTS COLD & WARM FRONTSCOLD & WARM FRONTS INTERPRETING SYNOPTIC CHARTSINTERPRETING SYNOPTIC CHARTS CLOUD FORMATION & RAINFALLCLOUD FORMATION & RAINFALL 4 DAY FORCASTS4 DAY FORCASTS SATELLITE IMAGESSATELLITE IMAGES

SeasonsSeasons As the Earth revolves As the Earth revolves around the Sun, it is tilted around the Sun, it is tilted on its axis at an angle of on its axis at an angle of 23.5 degrees.23.5 degrees.

In December when the In December when the southern hemisphere is tipped southern hemisphere is tipped towards the sun, more direct towards the sun, more direct sunlight and long hours of daylight cause sunlight and long hours of daylight cause warmer weather in June, when the southern hemisphere warmer weather in June, when the southern hemisphere is tipped away from the Sun.is tipped away from the Sun.

Australian WeatherAustralian Weather In terms of weather, Australia’s long In terms of weather, Australia’s long

coastline is unique in the world. It coastline is unique in the world. It stretches more than 3000km roughly along stretches more than 3000km roughly along the 35the 35thth parallel of latitude. parallel of latitude.

To the south, the southern Ocean extends To the south, the southern Ocean extends 3000km to the Antarctic continent. From 3000km to the Antarctic continent. From there, outbreaks of very cold polar air there, outbreaks of very cold polar air move northwards, warming somewhat as move northwards, warming somewhat as they pass over the ocean. The air is still they pass over the ocean. The air is still cool when it reaches Australia.cool when it reaches Australia.

Inland from the southern coast, a large Inland from the southern coast, a large proportion of the country is arid or semi-arid, proportion of the country is arid or semi-arid, with low rainfall and very hot summers.with low rainfall and very hot summers.

Air coming from the hot interior to the coast Air coming from the hot interior to the coast meets the cold air from Antarctica, giving meets the cold air from Antarctica, giving southern Australia highly variable weather.southern Australia highly variable weather.

Pressure systemsPressure systems

Atmospheric pressure varies with both Atmospheric pressure varies with both height above mean sea level, and from height above mean sea level, and from place to place at mean sea level.place to place at mean sea level.

Mean sea level pressure (MSLP) is Mean sea level pressure (MSLP) is measured in units called hectopascals measured in units called hectopascals (hPa).(hPa).

Lines on a weather map joining places of Lines on a weather map joining places of equal MSLP are called isobars.equal MSLP are called isobars.

On a daily weather map there will be On a daily weather map there will be patterns of relatively high and low patterns of relatively high and low pressure systems over Australia.pressure systems over Australia.

It is these systems that generate variations It is these systems that generate variations in wind, temperature and rainfall.in wind, temperature and rainfall.

In the southern hemisphere the wind flows In the southern hemisphere the wind flows clockwise around low pressure systems clockwise around low pressure systems and anti-clockwise around high pressure and anti-clockwise around high pressure systems.systems.

The strength or speed of the wind is The strength or speed of the wind is closely related to the spacing of isobars.closely related to the spacing of isobars.

Closer spacing means stronger winds.Closer spacing means stronger winds.

Air massesAir masses A large body of air originating in a A large body of air originating in a

particular place is called an air mass.particular place is called an air mass.

The boundary The boundary

line that line that

separates separates

2 air masses 2 air masses

is a front.is a front.

Air masses & weather mapsAir masses & weather maps

The main features of a weather map are:The main features of a weather map are:1.1. Isobars – generally drawn at intervals of 2 Isobars – generally drawn at intervals of 2

or 4 hPa, depending on the scale of the or 4 hPa, depending on the scale of the map.map.

2.2. Cold and warm fronts – major boundaries Cold and warm fronts – major boundaries between air masses. Shown as a bold line between air masses. Shown as a bold line with triangles for a cold fronts or semi-with triangles for a cold fronts or semi-circles for warm fronts.circles for warm fronts.

3.3. Troughs of low pressure – shown as Troughs of low pressure – shown as dashed lines.dashed lines.

4. Areas where rain has fallen in the past 12 or 4. Areas where rain has fallen in the past 12 or 24 hours, shown by hatching.24 hours, shown by hatching.

5. Surface wind direction and speed at spot 5. Surface wind direction and speed at spot locations – the direction from which the locations – the direction from which the wind is blowing is designated by the arrow wind is blowing is designated by the arrow shaft and the speed by the barbs along the shaft and the speed by the barbs along the shaft.shaft.

( a long barb = 20km/h, 2 long and 1 short ( a long barb = 20km/h, 2 long and 1 short barb = 50km/h)barb = 50km/h)

There are 2 main types of fronts; There are 2 main types of fronts;

– COLD FRONTS, and COLD FRONTS, and

– WARM FRONTS…WARM FRONTS…

Cold FrontsCold Fronts

In a cold front, an active wedge of cold air In a cold front, an active wedge of cold air undercuts a mass of warmer air. It moves undercuts a mass of warmer air. It moves under it because it is colder & more dense.under it because it is colder & more dense.

Cold fronts move at different speeds and Cold fronts move at different speeds and form a range of shapes.form a range of shapes.

They also produce many variations in They also produce many variations in weather depending on whether the warm air weather depending on whether the warm air was dry or moist.was dry or moist.

Cold front storm cloud

Summer cold front map

Warm FrontsWarm Fronts

Warm air is the more active part of the Warm air is the more active part of the system.system.

It moves in on the cooler air but because it It moves in on the cooler air but because it is less dense it is lighter and rides over it.is less dense it is lighter and rides over it.

The retreating cool air is replaced by the The retreating cool air is replaced by the warm air.warm air.

Warm fronts move much slower and the Warm fronts move much slower and the slope of the front is much less than in a cold slope of the front is much less than in a cold front.front.

http://www.bom.gov.au/nmoc/products/MSLP_B&W.shtml

The temperature, moisture content and The temperature, moisture content and other properties of an air mass reflect the other properties of an air mass reflect the region where it originated.region where it originated.

As it moves its properties are modified by As it moves its properties are modified by the surfaces it passes over.the surfaces it passes over.

Weather systemsWeather systems

Australia’s weather systems arrive Australia’s weather systems arrive from and move across the continent from and move across the continent West to EastWest to East

As a general rule in summer there are As a general rule in summer there are more high pressure systems and in more high pressure systems and in winter there are more low pressure winter there are more low pressure systemssystems

Weather chartWeather chartHigh pressure system

-generally calmer conditions

-Warmer

-wind flows anti-clockwise around high pressure system (red arrows) and spiralling slightly outwards

Weather chartWeather chartLow pressure system

- stronger winds, more unsettled conditions

-Colder

- wind travels in a clockwise direction around low pressure system and slightly inwards

-very deep low pressure systems may form into cyclones

Inflowing air associated with ‘lows’ result in Inflowing air associated with ‘lows’ result in convergence & ascent of air often resulting convergence & ascent of air often resulting in deep cloud formation and rainfall.in deep cloud formation and rainfall.

Outflowing air associated with ‘highs’ result Outflowing air associated with ‘highs’ result in divergence and descent of air and more in divergence and descent of air and more stable weather.stable weather.

BOM_AirBOM_Air pressure pressure

Typical Summer Weather MapTypical Summer Weather Map Northerly Northerly

winds over winds over eastern eastern AustraliaAustralia

Moist, easterly Moist, easterly flowflow

Cold frontCold front passing South passing South AustraliaAustralia

Typical Winter Weather MapTypical Winter Weather Map Deep low Deep low

pressure pressure system (972 system (972 hectopascals) hectopascals) south of south of TasmaniaTasmania

Very cold south Very cold south westerly air westerly air traveling traveling northwards northwards across Tas, Vic across Tas, Vic and SE NSWand SE NSW

Cool changesCool changes With a high pressure system over eastern With a high pressure system over eastern

Australia, the anti-clockwise air movement Australia, the anti-clockwise air movement brings an air mass from the hot dry interior brings an air mass from the hot dry interior over the southeast coastline. Temperatures over the southeast coastline. Temperatures under these north wind conditions are under these north wind conditions are typically around 40 degrees for several days.typically around 40 degrees for several days.

At these fronts, the hot northerly wind is At these fronts, the hot northerly wind is abruptly replaced by a cold south-westerly abruptly replaced by a cold south-westerly wind. Clockwise-flowing air moves towards wind. Clockwise-flowing air moves towards the front from the west. The arrival of the the front from the west. The arrival of the front can drop the temperature by 10 – 15 front can drop the temperature by 10 – 15 degrees in half an hour or less, with a further degrees in half an hour or less, with a further decrease in the next day or so.decrease in the next day or so.

Monitoring the weatherMonitoring the weather

Air pressure is probably the most important Air pressure is probably the most important weather element, because pressure weather element, because pressure variations drive the winds.variations drive the winds.

Daily weather map sequences show a Daily weather map sequences show a series of high and low pressure systems series of high and low pressure systems moving across the continent.moving across the continent.

Cloud formation & rainfallCloud formation & rainfall

Convective rainfall – when the earth’s Convective rainfall – when the earth’s surface is heated, air evaporates. As it rises surface is heated, air evaporates. As it rises it cools and condenses.it cools and condenses.

Eg. Rain on a hot summer afternoon, Eg. Rain on a hot summer afternoon, especially in the tropics. Often associated especially in the tropics. Often associated with huge anvil-topped clouds.with huge anvil-topped clouds.

Orographic rainfall – air is forced to rise Orographic rainfall – air is forced to rise when land barriers such as mountain ranges when land barriers such as mountain ranges lie in the path of air masses.lie in the path of air masses.

On the leeward side of the mountains, On the leeward side of the mountains, descending air is depleted of its moisture, descending air is depleted of its moisture, sometimes causing desert conditions.sometimes causing desert conditions.

Frontal rainfall – when moist air moves into Frontal rainfall – when moist air moves into a low pressure area or a front, clouds and a low pressure area or a front, clouds and rain may develop.rain may develop.

This type of rainfall is less violent that in This type of rainfall is less violent that in thunderstorms because the air rises more thunderstorms because the air rises more slowly and is cooled more gently.slowly and is cooled more gently.

It is also usually more widespread and It is also usually more widespread and protracted – eg. Dull grey overcast skies protracted – eg. Dull grey overcast skies and drizzly rain.and drizzly rain.

Satellite patterns to watch for:Satellite patterns to watch for: Cold front – long sweeping cloud, Cold front – long sweeping cloud,

sometimes with a spiral ‘hook’ cloud sometimes with a spiral ‘hook’ cloud shape.shape.

Severe thunderstorms – large ‘blobs’ of Severe thunderstorms – large ‘blobs’ of cloud.cloud.

Stratocumulus – large areas of uniform, Stratocumulus – large areas of uniform, lighter, low level clouds indicate overcast lighter, low level clouds indicate overcast and persistent drizzle.and persistent drizzle.

Air pressure is measured Air pressure is measured with a barometer.with a barometer.

Temperature is measured Temperature is measured with a thermometer.with a thermometer.

Humidity is the mass of water vapour in a Humidity is the mass of water vapour in a unit volume of air and is measured by a wet-unit volume of air and is measured by a wet-bulb thermometer (the warmer the air the bulb thermometer (the warmer the air the higher the humidity because the more water higher the humidity because the more water vapour it can hold.)vapour it can hold.)

Wind speed is measured with an Wind speed is measured with an anomometer.anomometer.

YOUR TASK:YOUR TASK: